Lab 3 Formal Report
Jason Kurkiewicz
EE 310 Sec 006
9/22
INTRODUCTION
In this lab, we worked on designing power supplies and voltage regulators onto our circuit boards. Separated into two sessions, we first constructed and tested a power supply followed by adding a voltage regulator with more tests. Our power supply was built off of a transformer that was given to us. The transformer was a source of 120VRMS with aturns ration of 12:1:1, giving us two input voltages of 10 VRMS. Using Design B, we were then expected to turn this into -12 VDC when leading to our eventual regulator and -5 0.5 VDC (w/ 15% ripple voltage) as an output after that.
CIRCUIT
Part I
The first elements we needed to apply to our circuit were two diodes, acting as rectifiers, which we sought from the data sheets to find the appropriate ones to use. After discovering the diodes we were to use, these were then added to the output of the transformer. Using the value of the voltage output and our test resistor, we found the test current to be .048A to help find these diodes.
Our next requirement was to find the filter capacitorvalue we needed to add in order to meet the ripple voltage range we were given. Using we discovered the appropriate capacitance to be 463, we then added the closest available capacitor to our circuit. Using a DMM and the oscilloscope, we found the max voltage, Vm, to be 13.6V and the ripple voltage, Vr, to be 1.4V. 1.4/13.6 * 100% = 10.3%, which is within the 15% we were given. Calculating the max current through one diode when on:
we found it to be 53mA. We then continued to calculate several aspects of the components within our circuit:
I (mA) / V (Volts) / P (Watts)Load Resistor / 94 / 13.6 / 1.28
Capacitor / 12 / 13.6 / .0435
Diode 1 / 53 / .032 / .0017
Diode 2 / 53 / .032 / .0017
figure 1. This schematic is the setup we used in part one. We were given design B which is this basic layout. As you can see, there are two reversed diodes connect to the output of the transformer, as well as a load resistor and capacitor connect in parallel. Pardon the poor quality as microsoft word isn’t the best for drawing schematics.
Part II
For part 2 of the lab we had further design and construction of the previous circuit. We continued by adding on a voltage regulator of our own and then a voltage regulator we were given and compared the two. Our self-made voltage regulator consisted of two resistors (one load) and a zener diode. The zener voltage we wished to achieve was -5.1 V. We searched for a zener diode data sheet to find which of the listed zener diodes we were to use for this desired voltage and found the 1N4733 was most appropriate. This zener diode was then connected in parallel with the load resistor and output. A second resistor was then added right from the negative output before the zener diode. In order to calculate the appropriate resistor to add, we needed to find the current we wanted. We were given a power of 0.5 W to go through our zener diode of -5.1 V. Using I = P/V, we discovered the max current through the diode (and resistor) to be 98 mA. We then used
to calculate an appropriate resistor. Thus, = 91.8. Next, we calculated a new load resistor that would have 30% of imax (68.6mA) run through it. Because this resistor is in parallel with the diode, its voltage would also be 5.1V. Thus, RL = 5.1V/.0686A = 74.3 . We then measured the voltages of the output with and without this load present. The voltage with no load was found as -5.04V, without was -4.37V, this was a %regulation of 13.3%.
After the work with our own constructed voltage regulator we then replaced it with a given regulator and compared. Again adding a load resistor so that we could force a max current of 98 mA and performing the same voltage checks, we found the %regulation to be 6.9%. Obviously slightly better results because this regulator was industrial made, however the result was still similar to our own voltage regulator.
R1
--
VinRLVL
++
Figure 2. This is the schematic for the voltage regulator that we constructed and added on to the power supply we constructed earlier. This circuit addition connects from the left (Vin) to the output from the previous task. You’ll notice the zener diode in parallel with the load resistor and R1 connected to the negative terminal of the input. Again, pardon the poor quality; desperate times call for desperate measures.
CONCLUSION
At the end of this lab, we had in front of us a power supply connect to a voltage regulator on our breadboard. With several calculations and searching through datasheets, we were able to apply the appropriate components to achieve results that we had hoped to see. With these two improvised circuits connected to a 120VRMS transformer, our task was to generate -12VDC leading into the voltage regulator and eventually a -5 VDC output in the end. As stated previously, our results were very successfully, as we saw an output of -5.04V without our load connected and -4.37 V with the load connected. We were also able to view a ripple voltage under 15% earlier in the lab as well, staying within the range we were assigned, which shows our circuit was able to control the AC voltage that had originally been supply from the transformer.